Growth comparisons of a supernodulating soybean (Glycine max) mutant and its wild‐type parent

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Abstract
The growth of a supernodulating, nitrate‐tolerant soybean [Glycine max (L.) Merr.] mutant nts382 (nitrate‐tolerant symbiosis) was compared to that of its wild‐type parent, cv. Bragg, over the first 50 days after sowing. Plants were grown either inoculated in the absence of an external nitrogen source or uninoculated in the presence of 5 mM KNO3. For both treatments, nts382 growth up to 13 days after planting was faster than that of cv. Bragg. Thereafter, supernodulation of inoculated nts382 occurred and growth of cv. Bragg was faster; shoot and root dry weight increments and leaf area were greater in cv. Bragg, but the N content of nts382 was higher. Relative growth and net assimilation rates were lower in nts382, which had faster shoot and root respiration rates. Shoot growth of uninoculated plants was similar for both mutant and wild‐type but roots of nts382 were slightly smaller than those of cv. Bragg. Total plant N content was similar in uninoculated cv. Bragg and nts382 but the latter had a higher leaf N content. Early lateral root formation (prior to nodule emergence) was greater in nts382 regardless of whether rhizobia or KJNO3 were present. We conclude that nts382 has some inherent differences from its parent but that supernodulation significantly retards plant growth.